We present the results of a submillimeter dust continuum study of
a molecular ridge in IC 5146 carried out at 850 μm and
450 μm with SCUBA on the James Clerk Maxwell Telescope
(JCMT). The mapped region is in size
() and consists of at least four dense
cores which are likely to be prestellar in nature. To study the
dust properties of the ridge and its embedded cores, we combined
the dust emission data with dust extinction data obtained by Lada
et al. (1999) from the NIR colors of background giant stars. The
ridge shows dust extinctions above ~10 mag, rising up to
35 mag in the cores. A map of dust temperatures, constructed from the continuum flux
ratios, shows significant temperature gradients: we find
temperatures of up to ~20 K in the outskirts and between
the cores, and down to ~10 K in the cores themselves. The
cores themselves are almost isothermal, although their average
temperatures vary between 10 K and 18 K. We used the
extinction data to derive in addition a map of the dust
emissivity parametrized by
. The average value of
agrees well with the canonical value of Mathis (1990).
We find that increases by a factor of from
to when the dust temperature
decreases from K to K. A Monte Carlo
simulation shows that this change is significant with regard to
the estimated calibration uncertainties. This is consistent with
models of dust evolution in prestellar cores by Ossenkopf &
Henning (1994) which predict that grain coagulation and the
formation of ices on grain surfaces in the cold, dense cloud
interiors lead to a significant increase of the m dust
opacity. This interpretation is furthermore supported by the
previous detection of gas-phase depletion of CO in one of the
IC 5146 cores (Kramer et al. 1999). Observations of dust fluxes
at short wavelengths are however needed to verify this result.

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